I finally cracked and bought an excellent condition used Canon 100mm F/2.8 L IS macro lens today.
I've been contemplating this for a long time, but put it off because my old Sigma 105mm f/2.8 EX DG Macro lens is optically superb, and has served me very well for many years.
Despite that, it has a few limitations inherent in its design - notably that the front barrel of the lens moves in and out as you focus or change magnification, which means it is relatively easy to crash into the subject, and the autofocus is essentially unusably slow, and very noisy.
This moving external part means that anything mounted to the filter thread applies stress to the mechanisms in the lens. Attaching my new macro flashguns felt very precarious, and I really wasn't comfortable with the risk of damaging a good lens by doing this.
The Canon lens has a fixed length barrel, with a fast, quiet, internal focusing mechanism, so it's a solid unit that's much more suited to the way I want to be able to work with the flashes.
While you often don't use AF in macro work, it's definitely a "nice to have" feature, and opens up some possibilities, especially in conjunction with the lens' other trick, image stabilisation.
I'm looking forward to putting this lens through its paces, both for macro and general distance work.
It seems that an unexpected benefit of staying with older, but IMHO still highly serviceable camera system is the relatively affordable availability of excellent lenses on the used market. The shop actually had two of these lenses in stock to choose from!
